The goal of this project is to understand the effects of ultrasound (US) on neural activity. US can modify action potential activity in neurons in vitro and in vivo without damaging neural tissue. This phenomenon can be applied in powerful new tools for basic and clinical neuroscience, with broad impact on public health issues related to mental and neurological disorders. To guide and hasten the development of these new tools, our research will provide insight into the physical, biophysical and neural mechanisms underlying US neurostimulation. Our approach is unique in combining technology development with mechanistic studies of US neurostimulation at levels of complexity ranging from the single cell to the whole animal. Our prior and preliminary results suggest that US radiation force causes tissue displacement, resulting in cell membrane strain and thereby affecting neural activity through changes in ion channel activity or neurotransmitter exocytosis. We will investigate this hypothesis by combining US neurostimulation with EEG recording and radiation force imaging in rats, optical displacement measurements and multielectrode recording in the salamander and rat retina in vitro and in vivo, and electrophysiological measurements of ion channel activity and exocytosis in single HEK and PC12 cells. We will also test alternative hypotheses related to two other physical effects of US, cavitation and heating. To distinguish these mechanisms from radiation force we will examine the dependence of US neurostimulation on frequency and intensity. To facilitate these experiments, we will develop and implement new US devices, allowing US to be applied with multifocal and micron-scale resolution. US neurostimulation is likely to have significant impact on public health. Brain stimulation therapies are used to treat Parkinson's disease, dystonia, and epilepsy and hold promise for many others. Compared to current brain stimulation techniques that rely on invasive implanted electrodes or have limited spatial resolution and depth penetration (e.g., transcranial magnetic stimulation), US offers an ideal combination of spatial resolution, depth penetration, and non-invasiveness. US neurostimlation can also be implemented in prosthetic devices; for example, to stimulate retinal circuitry to restore vision. In addition, US neurostimulation promises to become an enormously useful research tool in basic neuroscience, and is therefore relevant to all mental and neurological disorders of public health concern. However, all of these outcomes depend on the ability to apply US neurostimulation safely and with well-controlled, predictable results. Achieving this goal requires a detailed mechanistic understanding of US neurostimulation that our multidisciplinary research project will provide.